POS - Product Configurator No Variant

When a product with attributes is added in the Point of Sale, the configurator popup normally only shows the selected values as text. This module stores those selected attribute values on the order line and displays them in the Point of Sale order form.

• In the POS order form, the order lines list now has an optional column called "Extra Values" that shows the selected attribute values as tags. It is hidden by default and can be enabled from the column selector.
• The selected values are saved on the order line and sent to the backend when the order is synced, so they remain visible after the session is closed.
• The module also cleans up the stored values: if a value is no longer valid for the product (for example, the attribute was removed from the product), it is automatically removed from the order line.
• It works together with the standard Point of Sale product configurator and does not change prices or stock; it only records and displays the chosen options.

It touches the Point of Sale order (pos.order), order line (pos.order.line) and session (pos.session) models, and adds a small change to the POS order form view.